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    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<style>
    div {
        border: 1px solid black;
        margin: 25px;
        background-color: lightblue;
    }
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    <h1>简写属性 margin - 1 个值</h1>
    <div>div 元素的上、下、左、右外边距均为 25 像素。</div>
    <hr>
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